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llvm/lib/CodeGen/IfConversion.cpp

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//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the Evan Cheng and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the machine instruction level if-conversion pass.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "ifcvt"
#include "llvm/Function.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumSimple, "Number of simple if-conversions performed");
STATISTIC(NumSimpleRev, "Number of simple (reversed) if-conversions performed");
STATISTIC(NumTriangle, "Number of triangle if-conversions performed");
STATISTIC(NumDiamonds, "Number of diamond if-conversions performed");
STATISTIC(NumIfConvBBs, "Number of if-converted blocks");
namespace {
class IfConverter : public MachineFunctionPass {
enum BBICKind {
ICNotAnalyzed, // BB has not been analyzed.
ICReAnalyze, // BB must be re-analyzed.
ICNotClassfied, // BB data valid, but not classified.
ICSimple, // BB is entry of an one split, no rejoin sub-CFG.
ICSimpleFalse, // Same as ICSimple, but on the false path.
ICTriangle, // BB is entry of a triangle sub-CFG.
ICDiamond, // BB is entry of a diamond sub-CFG.
ICChild, // BB is part of the sub-CFG that'll be predicated.
ICDead // BB has been converted and merged, it's now dead.
};
/// BBInfo - One per MachineBasicBlock, this is used to cache the result
/// if-conversion feasibility analysis. This includes results from
/// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
/// classification, and common tail block of its successors (if it's a
/// diamond shape), its size, whether it's predicable, and whether any
/// instruction can clobber the 'would-be' predicate.
///
/// Kind - Type of block. See BBICKind.
/// NonPredSize - Number of non-predicated instructions.
/// IsAnalyzable - True if AnalyzeBranch() returns false.
/// ModifyPredicate - FIXME: Not used right now. True if BB would modify
/// the predicate (e.g. has cmp, call, etc.)
/// BB - Corresponding MachineBasicBlock.
/// TrueBB / FalseBB- See AnalyzeBranch().
/// BrCond - Conditions for end of block conditional branches.
/// Predicate - Predicate used in the BB.
struct BBInfo {
BBICKind Kind;
unsigned NonPredSize;
bool IsAnalyzable;
bool ModifyPredicate;
MachineBasicBlock *BB;
MachineBasicBlock *TrueBB;
MachineBasicBlock *FalseBB;
MachineBasicBlock *TailBB;
std::vector<MachineOperand> BrCond;
std::vector<MachineOperand> Predicate;
BBInfo() : Kind(ICNotAnalyzed), NonPredSize(0),
IsAnalyzable(false), ModifyPredicate(false),
BB(0), TrueBB(0), FalseBB(0), TailBB(0) {}
};
/// Roots - Basic blocks that do not have successors. These are the starting
/// points of Graph traversal.
std::vector<MachineBasicBlock*> Roots;
/// BBAnalysis - Results of if-conversion feasibility analysis indexed by
/// basic block number.
std::vector<BBInfo> BBAnalysis;
const TargetLowering *TLI;
const TargetInstrInfo *TII;
bool MadeChange;
public:
static char ID;
IfConverter() : MachineFunctionPass((intptr_t)&ID) {}
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual const char *getPassName() const { return "If converter"; }
private:
bool ReverseBranchCondition(BBInfo &BBI);
void StructuralAnalysis(MachineBasicBlock *BB);
bool FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Cond,
bool IgnoreTerm = false);
bool AttemptRestructuring(BBInfo &BBI);
bool AnalyzeBlocks(MachineFunction &MF,
std::vector<BBInfo*> &Candidates);
void ReTryPreds(MachineBasicBlock *BB);
bool IfConvertSimple(BBInfo &BBI);
bool IfConvertTriangle(BBInfo &BBI);
bool IfConvertDiamond(BBInfo &BBI);
void PredicateBlock(BBInfo &BBI,
std::vector<MachineOperand> &Cond,
bool IgnoreTerm = false);
void MergeBlocks(BBInfo &TrueBBI, BBInfo &FalseBBI);
// IfcvtCandidateCmp - Used to sort if-conversion candidates.
static bool IfcvtCandidateCmp(BBInfo* C1, BBInfo* C2){
// Favor diamond over triangle, etc.
return (unsigned)C1->Kind < (unsigned)C2->Kind;
}
};
char IfConverter::ID = 0;
}
FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
TLI = MF.getTarget().getTargetLowering();
TII = MF.getTarget().getInstrInfo();
if (!TII) return false;
DOUT << "\nIfcvt: function \'" << MF.getFunction()->getName() << "\'\n";
MF.RenumberBlocks();
BBAnalysis.resize(MF.getNumBlockIDs());
// Look for root nodes, i.e. blocks without successors.
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
if (I->succ_size() == 0)
Roots.push_back(I);
std::vector<BBInfo*> Candidates;
MadeChange = false;
while (true) {
// Do an intial analysis for each basic block and finding all the potential
// candidates to perform if-convesion.
bool Change = AnalyzeBlocks(MF, Candidates);
while (!Candidates.empty()) {
BBInfo &BBI = *Candidates.back();
Candidates.pop_back();
bool RetVal = false;
switch (BBI.Kind) {
default: assert(false && "Unexpected!");
break;
case ICReAnalyze:
// One or more of 'children' have been modified, abort!
case ICDead:
// Block has been already been if-converted, abort!
break;
case ICSimple:
case ICSimpleFalse:
DOUT << "Ifcvt (Simple" << (BBI.Kind == ICSimpleFalse ? " false" : "")
<< "): BB#" << BBI.BB->getNumber() << " ";
RetVal = IfConvertSimple(BBI);
DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
if (RetVal)
if (BBI.Kind == ICSimple) NumSimple++;
else NumSimpleRev++;
break;
case ICTriangle:
DOUT << "Ifcvt (Triangle): BB#" << BBI.BB->getNumber() << " ";
RetVal = IfConvertTriangle(BBI);
DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
if (RetVal) NumTriangle++;
break;
case ICDiamond:
DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " ";
RetVal = IfConvertDiamond(BBI);
DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
if (RetVal) NumDiamonds++;
break;
}
Change |= RetVal;
}
if (!Change)
break;
MadeChange |= Change;
}
Roots.clear();
BBAnalysis.clear();
return MadeChange;
}
static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
MachineBasicBlock *TrueBB) {
for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
E = BB->succ_end(); SI != E; ++SI) {
MachineBasicBlock *SuccBB = *SI;
if (SuccBB != TrueBB)
return SuccBB;
}
return NULL;
}
bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
if (!TII->ReverseBranchCondition(BBI.BrCond)) {
TII->RemoveBranch(*BBI.BB);
TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
std::swap(BBI.TrueBB, BBI.FalseBB);
return true;
}
return false;
}
/// StructuralAnalysis - Analyze the structure of the sub-CFG starting from
/// the specified block. Record its successors and whether it looks like an
/// if-conversion candidate.
void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
BBInfo &BBI = BBAnalysis[BB->getNumber()];
if (BBI.Kind == ICReAnalyze) {
BBI.BrCond.clear();
BBI.TrueBB = BBI.FalseBB = NULL;
} else {
if (BBI.Kind != ICNotAnalyzed)
return; // Already analyzed.
BBI.BB = BB;
BBI.NonPredSize = std::distance(BB->begin(), BB->end());
}
// Look for 'root' of a simple (non-nested) triangle or diamond.
BBI.Kind = ICNotClassfied;
BBI.IsAnalyzable =
!TII->AnalyzeBranch(*BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
if (!BBI.IsAnalyzable || BBI.BrCond.size() == 0)
return;
// Do not ifcvt if either path is a back edge to the entry block.
if (BBI.TrueBB == BB || BBI.FalseBB == BB)
return;
StructuralAnalysis(BBI.TrueBB);
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
// No false branch. This BB must end with a conditional branch and a
// fallthrough.
if (!BBI.FalseBB)
BBI.FalseBB = findFalseBlock(BB, BBI.TrueBB);
assert(BBI.FalseBB && "Expected to find the fallthrough block!");
StructuralAnalysis(BBI.FalseBB);
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
// Look for more opportunities to if-convert a triangle. Try to restructure
// the CFG to form a triangle with the 'false' path.
std::vector<MachineOperand> RevCond(BBI.BrCond);
bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
if (FalseBBI.FalseBB) {
if (TrueBBI.TrueBB && TrueBBI.TrueBB == BBI.FalseBB)
return;
std::vector<MachineOperand> Cond(BBI.BrCond);
if (CanRevCond &&
FalseBBI.TrueBB && FalseBBI.BB->pred_size() == 1 &&
FeasibilityAnalysis(FalseBBI, RevCond, true)) {
std::vector<MachineOperand> FalseCond(FalseBBI.BrCond);
if (FalseBBI.TrueBB == BBI.TrueBB &&
TII->SubsumesPredicate(FalseCond, BBI.BrCond)) {
// Reverse 'true' and 'false' paths.
ReverseBranchCondition(BBI);
BBI.Kind = ICTriangle;
FalseBBI.Kind = ICChild;
} else if (FalseBBI.FalseBB == BBI.TrueBB &&
!TII->ReverseBranchCondition(FalseCond) &&
TII->SubsumesPredicate(FalseCond, BBI.BrCond)) {
// Reverse 'false' block's 'true' and 'false' paths and then
// reverse 'true' and 'false' paths.
ReverseBranchCondition(FalseBBI);
ReverseBranchCondition(BBI);
BBI.Kind = ICTriangle;
FalseBBI.Kind = ICChild;
}
}
} else if (TrueBBI.TrueBB == FalseBBI.TrueBB && CanRevCond &&
TrueBBI.BB->pred_size() == 1 &&
FalseBBI.BB->pred_size() == 1 &&
// Check the 'true' and 'false' blocks if either isn't ended with
// a branch. If the block does not fallthrough to another block
// then we need to add a branch to its successor.
!(TrueBBI.ModifyPredicate &&
!TrueBBI.TrueBB && TrueBBI.BB->succ_size()) &&
!(FalseBBI.ModifyPredicate &&
!FalseBBI.TrueBB && FalseBBI.BB->succ_size()) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
// Diamond:
// EBB
// / \_
// | |
// TBB FBB
// \ /
// TailBB
// Note TailBB can be empty.
BBI.Kind = ICDiamond;
TrueBBI.Kind = FalseBBI.Kind = ICChild;
BBI.TailBB = TrueBBI.TrueBB;
} else {
// FIXME: Consider duplicating if BB is small.
bool TryTriangle = TrueBBI.TrueBB && TrueBBI.TrueBB == BBI.FalseBB &&
TrueBBI.BB->pred_size() == 1;
bool TrySimple = TrueBBI.BrCond.size() == 0 && TrueBBI.BB->pred_size() == 1;
if ((TryTriangle || TrySimple) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
if (TryTriangle) {
// Triangle:
// EBB
// | \_
// | |
// | TBB
// | /
// FBB
BBI.Kind = ICTriangle;
TrueBBI.Kind = ICChild;
} else {
// Simple (split, no rejoin):
// EBB
// | \_
// | |
// | TBB---> exit
// |
// FBB
BBI.Kind = ICSimple;
TrueBBI.Kind = ICChild;
}
} else if (FalseBBI.BrCond.size() == 0 && FalseBBI.BB->pred_size() == 1) {
// Try the other path...
std::vector<MachineOperand> RevCond(BBI.BrCond);
if (!TII->ReverseBranchCondition(RevCond) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
if (FalseBBI.TrueBB && FalseBBI.TrueBB == BBI.TrueBB &&
FalseBBI.BB->pred_size() == 1) {
// Reverse 'true' and 'false' paths.
ReverseBranchCondition(BBI);
BBI.Kind = ICTriangle;
FalseBBI.Kind = ICChild;
} else {
BBI.Kind = ICSimpleFalse;
FalseBBI.Kind = ICChild;
}
}
}
}
return;
}
/// FeasibilityAnalysis - Determine if the block is predicable. In most
/// cases, that means all the instructions in the block has M_PREDICABLE flag.
/// Also checks if the block contains any instruction which can clobber a
/// predicate (e.g. condition code register). If so, the block is not
/// predicable unless it's the last instruction. If IgnoreTerm is true then
/// all the terminator instructions are skipped.
bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Cond,
bool IgnoreTerm) {
// If the block is dead, or it is going to be the entry block of a sub-CFG
// that will be if-converted, then it cannot be predicated.
if (BBI.Kind != ICNotAnalyzed &&
BBI.Kind != ICNotClassfied &&
BBI.Kind != ICChild)
return false;
// Check predication threshold.
if (BBI.NonPredSize == 0 || BBI.NonPredSize > TLI->getIfCvtBlockSizeLimit())
return false;
// If it is already predicated, check if its predicate subsumes the new
// predicate.
if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Cond))
return false;
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
continue;
// TODO: check if instruction clobbers predicate.
if (!I->isPredicable())
return false;
}
return true;
}
/// AttemptRestructuring - Restructure the sub-CFG rooted in the given block to
/// expose more if-conversion opportunities. e.g.
///
/// cmp
/// b le BB1
/// / \____
/// / |
/// cmp |
/// b eq BB1 |
/// / \____ |
/// / \ |
/// BB1
/// ==>
///
/// cmp
/// b eq BB1
/// / \____
/// / |
/// cmp |
/// b le BB1 |
/// / \____ |
/// / \ |
/// BB1
bool IfConverter::AttemptRestructuring(BBInfo &BBI) {
return false;
}
/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
/// candidates. It returns true if any CFG restructuring is done to expose more
/// if-conversion opportunities.
bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
std::vector<BBInfo*> &Candidates) {
bool Change = false;
std::set<MachineBasicBlock*> Visited;
for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
MachineBasicBlock *BB = *I;
StructuralAnalysis(BB);
BBInfo &BBI = BBAnalysis[BB->getNumber()];
switch (BBI.Kind) {
case ICSimple:
case ICSimpleFalse:
case ICTriangle:
case ICDiamond:
Candidates.push_back(&BBI);
break;
default:
Change |= AttemptRestructuring(BBI);
break;
}
}
}
// Sort to favor more complex ifcvt scheme.
std::stable_sort(Candidates.begin(), Candidates.end(), IfcvtCandidateCmp);
return Change;
}
/// isNextBlock - Returns true either if ToBB the next block after BB or
/// that all the intervening blocks are empty.
static bool isNextBlock(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
MachineFunction::iterator I = BB;
MachineFunction::iterator TI = ToBB;
MachineFunction::iterator E = BB->getParent()->end();
while (++I != TI)
if (I == E || !I->empty())
return false;
return true;
}
/// ReTryPreds - Invalidate predecessor BB info so it would be re-analyzed
/// to determine if it can be if-converted.
void IfConverter::ReTryPreds(MachineBasicBlock *BB) {
for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
E = BB->pred_end(); PI != E; ++PI) {
BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
PBBI.Kind = ICReAnalyze;
}
}
/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
///
static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
const TargetInstrInfo *TII) {
std::vector<MachineOperand> NoCond;
TII->InsertBranch(*BB, ToBB, NULL, NoCond);
}
/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
///
bool IfConverter::IfConvertSimple(BBInfo &BBI) {
bool ReverseCond = BBI.Kind == ICSimpleFalse;
BBI.Kind = ICNotClassfied;
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
BBInfo *CvtBBI = &TrueBBI;
BBInfo *NextBBI = &FalseBBI;
std::vector<MachineOperand> Cond(BBI.BrCond);
if (ReverseCond) {
std::swap(CvtBBI, NextBBI);
TII->ReverseBranchCondition(Cond);
}
PredicateBlock(*CvtBBI, Cond);
// If the 'true' block ends without a branch, add a conditional branch
// to its successor unless that happens to be the 'false' block.
if (CvtBBI->IsAnalyzable && CvtBBI->TrueBB == NULL) {
assert(CvtBBI->BB->succ_size() == 1 && "Unexpected!");
MachineBasicBlock *SuccBB = *CvtBBI->BB->succ_begin();
if (SuccBB != NextBBI->BB)
TII->InsertBranch(*CvtBBI->BB, SuccBB, NULL, Cond);
}
// Merge converted block into entry block. Also add an unconditional branch
// to the 'false' branch.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, *CvtBBI);
if (!isNextBlock(BBI.BB, NextBBI->BB))
InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
// Update block info. BB can be iteratively if-converted.
BBI.Kind = ICReAnalyze;
ReTryPreds(BBI.BB);
CvtBBI->Kind = ICDead;
// FIXME: Must maintain LiveIns.
return true;
}
/// IfConvertTriangle - If convert a triangle sub-CFG.
///
bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
BBI.Kind = ICNotClassfied;
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
// Predicate the 'true' block after removing its branch.
TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
PredicateBlock(TrueBBI, BBI.BrCond);
// If 'true' block has a 'false' successor, add an exit branch to it.
bool HasEarlyExit = TrueBBI.FalseBB != NULL;
if (HasEarlyExit) {
std::vector<MachineOperand> RevCond(TrueBBI.BrCond);
if (TII->ReverseBranchCondition(RevCond))
assert(false && "Unable to reverse branch condition!");
TII->InsertBranch(*BBI.TrueBB, TrueBBI.FalseBB, NULL, RevCond);
}
// Join the 'true' and 'false' blocks if the 'false' block has no other
// predecessors. Otherwise, add a unconditional branch from 'true' to 'false'.
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
bool FalseBBDead = false;
if (!HasEarlyExit && FalseBBI.BB->pred_size() == 2) {
MergeBlocks(TrueBBI, FalseBBI);
FalseBBDead = true;
} else if (!isNextBlock(TrueBBI.BB, FalseBBI.BB))
InsertUncondBranch(TrueBBI.BB, FalseBBI.BB, TII);
// Now merge the entry of the triangle with the true block.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, TrueBBI);
std::copy(BBI.BrCond.begin(), BBI.BrCond.end(),
std::back_inserter(BBI.Predicate));
// Update block info. BB can be iteratively if-converted.
BBI.Kind = ICReAnalyze;
ReTryPreds(BBI.BB);
TrueBBI.Kind = ICDead;
if (FalseBBDead)
FalseBBI.Kind = ICDead;
// FIXME: Must maintain LiveIns.
return true;
}
/// IfConvertDiamond - If convert a diamond sub-CFG.
///
bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
BBI.Kind = ICNotClassfied;
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
SmallVector<MachineInstr*, 2> Dups;
if (!BBI.TailBB) {
// No common merge block. Check if the terminators (e.g. return) are
// the same or predicable.
MachineBasicBlock::iterator TT = BBI.TrueBB->getFirstTerminator();
MachineBasicBlock::iterator FT = BBI.FalseBB->getFirstTerminator();
while (TT != BBI.TrueBB->end() && FT != BBI.FalseBB->end()) {
if (TT->isIdenticalTo(FT))
Dups.push_back(TT); // Will erase these later.
else if (!TT->isPredicable() && !FT->isPredicable())
return false; // Can't if-convert. Abort!
++TT;
++FT;
}
// One of the two pathes have more terminators, make sure they are
// all predicable.
while (TT != BBI.TrueBB->end()) {
if (!TT->isPredicable()) {
return false; // Can't if-convert. Abort!
}
++TT;
}
while (FT != BBI.FalseBB->end()) {
if (!FT->isPredicable()) {
return false; // Can't if-convert. Abort!
}
++FT;
}
}
// Remove the duplicated instructions from the 'true' block.
for (unsigned i = 0, e = Dups.size(); i != e; ++i) {
Dups[i]->eraseFromParent();
--TrueBBI.NonPredSize;
}
// Merge the 'true' and 'false' blocks by copying the instructions
// from the 'false' block to the 'true' block. That is, unless the true
// block would clobber the predicate, in that case, do the opposite.
BBInfo *BBI1 = &TrueBBI;
BBInfo *BBI2 = &FalseBBI;
std::vector<MachineOperand> RevCond(BBI.BrCond);
TII->ReverseBranchCondition(RevCond);
std::vector<MachineOperand> *Cond1 = &BBI.BrCond;
std::vector<MachineOperand> *Cond2 = &RevCond;
// Check the 'true' and 'false' blocks if either isn't ended with a branch.
// Either the block fallthrough to another block or it ends with a
// return. If it's the former, add a branch to its successor.
bool NeedBr1 = !BBI1->TrueBB && BBI1->BB->succ_size();
bool NeedBr2 = !BBI2->TrueBB && BBI2->BB->succ_size();
if ((TrueBBI.ModifyPredicate && !FalseBBI.ModifyPredicate) ||
(!TrueBBI.ModifyPredicate && !FalseBBI.ModifyPredicate &&
NeedBr1 && !NeedBr2)) {
std::swap(BBI1, BBI2);
std::swap(Cond1, Cond2);
std::swap(NeedBr1, NeedBr2);
}
// Predicate the 'true' block after removing its branch.
BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
PredicateBlock(*BBI1, *Cond1);
// Add an early exit branch if needed.
if (NeedBr1)
TII->InsertBranch(*BBI1->BB, *BBI1->BB->succ_begin(), NULL, *Cond1);
// Predicate the 'false' block.
PredicateBlock(*BBI2, *Cond2, true);
// Add an unconditional branch from 'false' to to 'false' successor if it
// will not be the fallthrough block.
if (NeedBr2 && !isNextBlock(BBI2->BB, *BBI2->BB->succ_begin()))
InsertUncondBranch(BBI2->BB, *BBI2->BB->succ_begin(), TII);
// Keep them as two separate blocks if there is an early exit.
if (!NeedBr1)
MergeBlocks(*BBI1, *BBI2);
// Remove the conditional branch from entry to the blocks.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
// Merge the combined block into the entry of the diamond.
MergeBlocks(BBI, *BBI1);
// 'True' and 'false' aren't combined, see if we need to add a unconditional
// branch to the 'false' block.
if (NeedBr1 && !isNextBlock(BBI.BB, BBI2->BB))
InsertUncondBranch(BBI1->BB, BBI2->BB, TII);
// If the if-converted block fallthrough or unconditionally branch into the
// tail block, and the tail block does not have other predecessors, then
// fold the tail block in as well.
BBInfo *CvtBBI = NeedBr1 ? BBI2 : &BBI;
if (BBI.TailBB &&
BBI.TailBB->pred_size() == 1 && CvtBBI->BB->succ_size() == 1) {
CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
BBInfo TailBBI = BBAnalysis[BBI.TailBB->getNumber()];
MergeBlocks(*CvtBBI, TailBBI);
TailBBI.Kind = ICDead;
}
// Update block info.
TrueBBI.Kind = ICDead;
FalseBBI.Kind = ICDead;
// FIXME: Must maintain LiveIns.
return true;
}
/// PredicateBlock - Predicate every instruction in the block with the specified
/// condition. If IgnoreTerm is true, skip over all terminator instructions.
void IfConverter::PredicateBlock(BBInfo &BBI,
std::vector<MachineOperand> &Cond,
bool IgnoreTerm) {
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
continue;
if (TII->isPredicated(I))
continue;
if (!TII->PredicateInstruction(I, Cond)) {
cerr << "Unable to predicate " << *I << "!\n";
abort();
}
}
BBI.NonPredSize = 0;
NumIfConvBBs++;
}
/// TransferPreds - Transfer all the predecessors of FromBB to ToBB.
///
static void TransferPreds(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
for (MachineBasicBlock::pred_iterator I = FromBB->pred_begin(),
E = FromBB->pred_end(); I != E; ++I) {
MachineBasicBlock *Pred = *I;
Pred->removeSuccessor(FromBB);
if (!Pred->isSuccessor(ToBB))
Pred->addSuccessor(ToBB);
}
}
/// TransferSuccs - Transfer all the successors of FromBB to ToBB.
///
static void TransferSuccs(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
for (MachineBasicBlock::succ_iterator I = FromBB->succ_begin(),
E = FromBB->succ_end(); I != E; ++I) {
MachineBasicBlock *Succ = *I;
FromBB->removeSuccessor(Succ);
if (!ToBB->isSuccessor(Succ))
ToBB->addSuccessor(Succ);
}
}
/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
///
void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
ToBBI.BB->splice(ToBBI.BB->end(),
FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
// If FromBBI is previously a successor, remove it from ToBBI's successor
// list and update its TrueBB / FalseBB field if needed.
if (ToBBI.BB->isSuccessor(FromBBI.BB))
ToBBI.BB->removeSuccessor(FromBBI.BB);
// Redirect all branches to FromBB to ToBB.
std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
FromBBI.BB->pred_end());
for (unsigned i = 0, e = Preds.size(); i != e; ++i)
Preds[i]->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
// Transfer preds / succs and update size.
TransferPreds(ToBBI.BB, FromBBI.BB);
TransferSuccs(ToBBI.BB, FromBBI.BB);
ToBBI.NonPredSize += FromBBI.NonPredSize;
FromBBI.NonPredSize = 0;
}
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